In field desorption mass spectrometry, a positive ion beam is generated in a mass spectrometer by causing electrons to tunnel to the emitting point while positive ions are ejected from the emitter along field lines into the optical system of the mass spectrometer. Molecules of sample material applied to the emitter may thus be analyzed even though they may be of very low vapor pressure and very high molecular weight. To maximize the emitter efficiency, a large number of uniformly-spaced points of approximately equal height above the emitter substrate are necessary. Additionally, to facilitate cleaning, the emitter should be thermally stable to relatively high temperature.
Heretofore, the best emitters have been provided by vapor-depositing carbon dendrites on a tungsten substrate. However, these devices are inherently fragile, have relatively short useful lives, tend to adhere to sample materials, and because of random orientation of the dendrites have non-uniform field gradients and limited heat transport to active emitter points.